BMW 116i (2.0litre N43) rough idle.

[CHARLESBERG]

Evening all,

Sorry to be a pain but I have posted this in both BMW general and here, not sure where will be best?

Looking for some advice with my wifes 2009 116i (2.0litre N43) which is currently suffering from a rough idle on a cold engine start up. It idles rough and the whole car vibrates but is fine after a couple of minutes warming up; no obvious signs of a misfire.

I have carried out some research on the web, seems to be a fair amount of people suffering similar symptoms on various BMW petrol engines- a few people have changed various sensors, plugs, engine mounts but it seems always end up at the injectors. I have spoken to BMW UK today, this particular car hasn't ever had a recall for injectors (this seemed to be the case in the US on the 335i engine for similar symptoms) although it has been in prior to our ownership for the ignition coils which were recalled at some point. Not exactly sure what parts would have been changed?

I have spoken to an independent garage as it is due a service, they have initially suggested either injectors or inlet coked up from what I told them on the phone. It hasn't currently been plugged in to a diagnostics machine but i'm not 100% sure these point you in the right direction.

Current thoughts are have injectors removed, sent away to be cleaned and 'tested' to be advised if they've failed or they also suggested a walnut blast.

I don't honestly have much experience in either of these, I instantly dismissed the walnut blast assuming it was 'snake oil' but after watching a couple of youtube videos it looks like it can actually do something positive. I am reluctant to say the injectors to be changed straight away as I was quoted £180 each x 4 off. A quick look around the internet indicates this is a fair price, although leaning towards having them tested (£60 for four I think with labour on top) as it seems to be only two of them usually go, then replace if required.

If the car needs the money spending on it, then we can get the work done but I will be slightly miffed if we plow a substantial amount of money into a car that has enough rattly body trim as it is and we don't get anywhere. If you think I have got the wrong end of the stick and it could be something else, please let me know.

All advice / experience greatly appreciated...

Thanks,
Charlie.

[GreenV8S]

CHARLESBERG said:

currently suffering from a rough idle on a cold engine start up

it is due a service

Could be something simple like dirty plugs so I'd have the service before spending any more money trying to diagnose it. And if I was going ahead trying to diagnose it, my first step would be to try to work out whether it is a single cylinder misfire (the symptoms hint at that) and if so which cylinder is affected. Header temps after a cold start would be the first thing to check.